2.4.3 Osmosis

Question 1

All cells are surrounded by a cell membrane which is, what?

Answer 1

partially permeable

Question 2

Osmosis allows water to, what?

Answer 2

move in and out of cells by osmosis

Question 3

What is Osmosis

Answer 3

Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane

In doing this, water is moving down its concentration gradient

Question 4

Because the cell membrane is partially permeable, what does that mean?

Answer 4

it allows small molecules (like water) through but not larger molecules (like solute molecules)

Question 5

What type of water potential does Dilute Solution have

Answer 5

dilute solution has a high water potential

Question 6

What type of water potential does a concentrated solution have

Answer 6

low water potential

Question 7

(Exam Tip) Osmosis refers only to what?

Answer 7

the movement of water molecules, so if in an exam you are talking about the movement of water, make sure you mention osmosis as this will often earn you a mark

The best explanations to do with osmosis will refer to water potential.

Question 8

As a result of Osmosis what happens to animal cells

Answer 8

Animal cells lose and gain water as a result of osmosis

Question 9

In animal cells, the results of osmosis can be severe, why?

Answer 9

As animal cells do not have a supporting cell wall, the results of osmosis can be severe

Question 10

If an animal cell is placed into a strong sugar solution(with a lower water potential than the cell) , what happens?

Answer 10

it will lose water by osmosis and become crenated (shriveled up)

Question 11

If an animal cell is placed into distilled water (with a higher water potential than the cell) what will happen?

Answer 11

it will gain water by osmosis as it has no cell wall to create turgor pressure

It will continue to gain water until the cell membrane is stretched too far and it bursts

Question 12

Why is it important that Osmosis is carefully controlled in organisms

Answer 12

It is important that osmosis is carefully controlled in organisms to avoid damage to cells through lysis

Question 13

What is Lysis

Answer 13

the breaking down of the membrane of a cell

Question 14

What is osmoregulation

Answer 14

The Homeostatic control of the water potential across membranes within the body

Question 15

The human body is adapted to maintain the optimum, what?

Answer 15

osmotic balance

Question 16

What process does the human body do to maintain the optimum osmotic balance

Answer 16

using processes such as sweating or increasing and decreasing urine concentration

Question 17

as a result of osmosis, what do plants do

Answer 17

Plant cells lose or gain water as a result of osmosis

Question 18

As plant cells have a supporting cell wall, what are they protected from?

Answer 18

they are protected from cell lysis

Question 19

If a plant cell is placed into a strong sugar solution, what will happen?

Answer 19

it will lose water by osmosis

Question 20

What happens to a plant cell if they lose water by osmosis

Answer 20

The vacuole gets smaller and the cell membrane shrivels away from the cell wall

It becomes flaccid or plasmolyzed (shrivelled up)

Question 21

If a plant cell is placed into distilled water (with a higher water potential than the cell), what happens?

Answer 21

it will gain water by osmosis

Question 22

When the plant cell gains water by osmosis what happens

Answer 22

The vacuole gets bigger, pushing the cell membrane against the cell wall

The plant cell is described as being turgid or as containing a high turgor pressure (the pressure of the cytoplasm pushing against the cell wall)

Question 23

Water entering the cell by osmosis makes the cell, what?

Answer 23

makes the cell rigid and firm

Question 24

Why is it important for water to enter the plant cell

Answer 24

to provide support and strength for the plant – making the plant stand upright with its leaves held out to catch sunlight

Question 25

If plants do not receive enough water, what happens to it?

Answer 25

the cells cannot remain rigid and firm (turgid) and the plant wilts

Question 26

In hypertonic solution red blood cells have:

Answer 26

Red Blood Cells have higher water potential than solution.

Net movement of water out

Shrivelled cells

Question 27

In isotonic solution red blood cells are:

Answer 27

The water potential is equal between red blood cells and solution

No net movement of water

Normal Cells

Question 28

In hypertonic solution red blood cells have:

Answer 28

Red blood cells have lower water potential than solution

Net movement of water in

Cells swell, may lyse (burst)